Preparation of paper-making fiber and other useful materials from straw



Oct. 26, 1948. s. D. WELL-s 2,452,533

. PREPARATION oF PAPER-MAKING FIBER AND OTHER USEFUL MATERIALS FROM sTRAw 'Filed June 50, 1944 Patented Oct. 26, 1948 UNITED ISTAT-151s 4Pli'rerrr oFFlci-z PREPARATION F PAPER-MAKING FIBER AND OTHER USEFUL MATERIALS FROM STRAW Sidney D. Wells, Combined Locks, Wis., assignor to The Institute of Paper Chemistry, Appleton, Wis., a corporation of Wisconsin Application June 30, 1944, Serial No. 542,987

Certain types of straw, and particularly fiax straw, which result as by-products from a seedV crop, contain a substantial percentage of useful liber. For example, the straw of the flax plant contains a fiber known as bast fiber which is particularly suitable for use in making certain high grade papers and textiles.

Where flax or similar crops are used for the purpose of producing a seed crop, the methods of cultivation and crop treatmentl are such that it is not ordinarily commercially feasible to make use of the fiber for textile purposes. However, methods of utilizing such straws, for example, as

Y Adisclosed in my former patent above referred to,

have been devised for the purpose of making such bers available for use in the manufacture of high-grade paper, for instance cigarette paper.

I have discovered that not only is it possible to recover from straws of .the type referred to a large percentage of fiber in the form of rstclass paper-making material, but also that the other constituents of the straw can be classified into more valuable'and less valuable components. For example, the non-fibrous fines, which can be produced as a by-product of my improved process, contain about six per cent of protein and are therefore capable of use as an lingredient v of stock or poultry food.

In practicing the improved process, the dry straw is rst subjected to a percussive treatment in any suitable type of equipment, for'example a rod mill, and the product of such percussive treatment, or preferably so much of the product as will pass through a rather coarse screen-of about 2 mesh, or more or less, depending upon the material and conditions, is subjected to a combined screening and pneumatic classification process, the screen employed being rather coarse, for example around 8 mesh, or more or less, depending upon the material and conditions. While the material is passing over the screen, it is acted upon by a counter-current of air of suflicient pressure and volume, so that the claims. (ci. 19-5) lighter particles of fiber and other product of the rod mill are air borne and do not pass through the screen, although of less dimensions than the size of the mesh.

In this way, there is screened out from the rod mill product all of the relatively heavy particles of shive or non-fibrous material, but the lighter ber particles `and the finer shive particles or fines are air borne, and therefore not screened out along with the heavy shive parts.

Usually, it is found desirable to subject the material, in its passage over the 8 mesh screen,

to considerable agitation so as to effect proper screening. A certain amount of agitation isripro-- vided by the action of thematerialas it pass/es over the screen, and this action is materially assisted by the counter-current of air passing up through the screen. However, it will ordinarily be found advantageous to employ a screen of the vibrating 0r gyratory type of which there are many types available for this particular purpose.

At this point, it may be stated that I have discovered that, if the rod mill product has been properly treated in the rod mill, so that it will all pass through the openings of a half inch mesh screen, in such material substantially all of the shive"` particles have been detached from the fiber and, although some fiberv particles or bunches may fbe of a size which will not pass -through ang mesh screen, on the other hand,

practically allof the shive is in 'particles less than 8 mesh in size. In other words, the rod mill treatment effects a-,sulbstantially complete' separation between the fiber and the shive leaving most of the shive in condition to pass through the 8 mesh screen.

However, the rod mill treatment also produces some .small portions of ber and small shive portions of various sizes collectively designated as fines, all of which are capable of `passing the 8 mesh screen; the counter current of air provided at the screen prevents the loss of these fine particles at the 8 mesh screen, and in addition accomplishes the agitation function previously described. Therefore, the material which passes beyond the 8 mesh screen is found to consist substantially of fiber particles or bunches of various n a 40 mesh screen, which serves to screen out the non-fibrous material, leaving the fiber on the 3 top of the screen. This fiber which results as the main product of the process is used for paperbe described, pipe is subjected to an upward ,/fsuction, and hencevthere will be an up-draft of making in the same manner as the fiber proif duced in accordance with my prior Patent No. 2,298,994. Additional intermediate separations and classications are within the contemplation of the invention, as will hereinafter appear, but the foregoing outlines the basic steps of the separation process of the invention.

It will be seen, therefore, that the products of the process consist of fiber, coarse shive and fines, the dust being usually considered a part of the fines. Although in certain instances, under vcertain conditions, it may be possible to separate the rines from the rod mill product prior to the separation of the coarse shive particles, it is advisable to postpone this step until after the coarse shive has been removed, as above described.

Specific example In applying the invention to the treatment of the straw resulting from the production of a crop of flax seeds, it is desirable to use an apparatus of the general stype disclosed in the drawing accompanying this application.

Referring tc the drawings, I represents a conventional type of rod mill in which the percussive treatment is effected. Said rod mill is fed with flax straw by a suitable feeder such as a screw conveyor 2, which receives the raw material through the hopper 3. For reasons of economy and production of a high-grade product, it is not advisable to carry the percussive treatment in the rod mill to such an extent as to complete the percussive treatment on 100% of the material, and therefore it is preferred not to equip the rod mill with a screen, but to,use a screen on the discharge, and return the over-size to the inlet of the rod mill for further treatment. This is done 1by permitting the material discharged from the rod mill to feed rather freely into the discharge hood 4 at the lower end of which is an opening 5 to an enclosed chute 6 equipped with a pair of gyratory screens 'I and 8. The upper screen may be of approximately 2 mesh, while the lower screen is of about 8 mesh. It maybe assumed that any product which is not capable of passing through the 2 mesh screen probably includes the fiber and shive components which have not been sufficiently worked in the rod mill to fracture the bond between the shive and the fiber, and therefore these larger particles are allowed to pass on to a spout 9 equipped with a suitable air seal I0 and fall onto the upper stretch II of a belt conveyor. These over-size particles of rod mill product are then delivered to the boot I2 of an elevator I3, and delivered from the elevator spout I4 into the feed hopper 3 previously referred to. In this manner, the oversized particles are re-cycled for re-treatment. A y

The selected product which passes through the 2 mesh screen drops onto the lower 8 mesh screen, and the heavy or coarse shive parts pass through the 8 mesh screen into a funnel I5 reaching into the top of a closed bin I6. In the top wall of said bin there is inserted a pipe I1 -by means of which air may enter the bin IB. However, the flow of air through pipe I1 may be regulated by a damper I8. Y v

That portion of the chute 6 which is located between the 2 mesh and the 8 mesh screen, at its lower end communicates freely with a discharge air through the 8 mesh screen 8, the control of said suction being effected by damper I8. Hence only the coarse shive parts willl pass through the screen 8, the remainder of the material consisting of fiber and shive nes being saved and sucked upward through pipe 20.

The pipe 20, at its upper end, discharges tangentially into the upper or large diameter portion of a cone classifier or cyclone 2I, the vent or discharge '22 of which is connected into the eye of a centrifugal fan 23. Said fan constitutes the means for subjecting the uptake pipe 2li to the required suction. In certain instances, it may be advisable to connect the upper end of the hood 4 directly with the upper portion of pipe 20 by means of a by-pass 24 controlled by a suitable damper 25. By this means, it is possible to provide a short cut path of movement for the extremely fine particles such as dust or other light material which go direct to the classifier or cyclone 2I without having to pass through the chute 6 and up pipe 20. The amount of said by-pass effect can, of course, be regulated by adjustment of the damper 25.

pipe I9 which, in turn, is connected to the lower The discharge 26 from the bottom of the cyclone or classifier 2| enters a chute 21 .within which there is located a 40 mesh shaking or gyratory screen. 28, this screen being of substantially the correct mesh to screen out the desired ber from the material discharged from the classifier 2I.

That part of the chute 21 which is located above the 40 mesh screen is connected to a discharge duct 29 which enters the closed fiber bin 30, in which the ber is accumulated and withdrawn from time to time. That part of the chute 21 which is below the 40 mesh screen 28 leads into a separate discharge pipe 3I leading into a closed bin 32 for receiving the shive fines.

In certain cases, it may be feasible to lead the discharge 33 of the exhaust fan 23 directly into the' atmosphere. However, on account of the fact that it may be advisable to save the powder-like nes as well as the fines of larger size, it is pre-V 32 through a suitable air seal 31.

I claim:

i. The improved method of obtaining a selected useful fiber from a flax straw which comprises the steps of fracturing the bond between the straw ber and shive so as to produce a mixture of relatively large particles of shive, relatively smaller and lighter particles of shive, the selected ber in various lengths, and dust, separating the large particles of shive from the selected 'ber and the other constituents of the said mixture by passing the mixture over a screen while subjecting the mixture to a counter current of air of such intensity that the large particles of shive are able to pass through the screen by gravity, whereas the ne particles of fiber, the fine shive particles, and the dust are restrained from passing through the screen, and subsequently separating theselected fiber from the material which is restrained from passing through said screen by a process which includes a second screening operation.

2. The improved method of obtaining a seaesaase lected useful ber from a ilax straw which comprises the steps of fracturing the bond between the straw fiber and shive so as to produce a mixture of relatively large particles of shive, relatively smaller and lighter particles of shive, the selected ber in various lengths, and dust, separating the large particles of shive from the selected fiber and the other constituents of the said mixture, by passing the mixture over a, mechanically agitated screen while subjecting the mixture to a counter current of air of such intensity that the large particles of shive are able to pass through the screen lby gravity whereas the fine particles of shive, the ne particles of ber, and the dust are restrained from passing through the screen, and subsequently separating the selected fiber from the material rwhich is restrained from passing through said screen by a second screening operation involving the use of a second mechanically agitatedl screen having a sufficiently ne mesh toscreen out the desired fiber.

3. The improved method of obtaining bast ber from flax straw, which comprises the steps of percussively treating said flax straw to fracture the bond between the bast fiber and the straw shive so as to produce a mixture of relatively large particles of shive, relatively smaller and in various lengths, and dust, separating the large particles of shive from the bast fiber and the- -other constituents of said mixture by passing the mixture over a mechanically agitated screen of about 8 mesh while subjecting the mixture to a counter current of air of such intensity that the large particles of shive are able to passl through the screen by gravity, whereas the fine particles of bast fiber, the ne shive particles, and the dust are restrained from passing through the screen, subsequently Aeffecting further separation by pneumatic means of the bast nber from the mixture which is restrained from passing through .said screen, and finally effecting substantially relatively smaller particles of shive, and dust,pro`

viding a zone of low pressure adjacent said percussivezone for drawing said decorticated mixture from said percussive zone as saidv straw is broken up, continuously withdrawing air, rela'- tively light particles of ber and dust from the the same to a pneumatic separating zone, con tinously withdrawing the remainder of said de corticated mixture by gravity from the bottom of said zone of low pressure, the material which is withdrawn from the lbottom of said zone of low pressure being conducted in sequence through a;

first screening zone, which includes a coarse mesh screen, and a second screening zone in which said material is passed across a screen ot lighter particles of shive, the desired bast liber substantially finer mesh while being subjected to a countercurrent of air of such intensity that the large particles of shive pass through said screen by gravity to a discharge point, while relatively light particles of fiber, relatively smaller parti- -as to convert the straw into a decorticated mixture which includes relatively light particles of ber, relatively large particles of shive and straw, relatively smaller particles ofv shive, and dust, providing a zone oflow pressure adjacent said percussive zone for drawing said decorticated mixture from said percussive zone as said straw is broken up, continuously withdrawing air, relatively light particles of ber and dust from the 'top of said zone of low pressure and conducting the same to a pneumatic separating zone, continuously withdrawing the remainder of said decorticated mixture by` gravity from the bottom of said zone of low'pressure, the material which is withdrawn from the bottom of said zone of low pressure being conducted in sequence through a first screening zone, Which-includes avmechanically agitated screen of about 2 mesh, and a second screening zone in which said material is t the material retained in said pneumatic separating zone by withdrawing the dust and passing the remaining materialover a mechanically agitated screen of about 40 mesh to remove the relatively 'I smaller particles oi shive. v

v top of'said zone oi low pressure and conducting SIDNEY D. WELLS.

' REFERENCES CITED The following references are of record in the ille ofthis patent: l

UNITED STATES PATENTS wens oct. 1a, 1943 

